OBJECTIVES: According to PhRMA, 75% of Americans are non-adherent on one or more of their medications. Low adherence leads to worsening of the disease and unnecessary health care spending. Various tools have been used by health care professionals to improve medication adherence. The objective of this study is to conduct a systematic review to identify tools used to improve medication adherence and their impact on medication adherence.  METHODS: PRISMA guidelines were followed for conducting a systematic review. A comprehensive electronic search of research databases (PubMed, MEDLINE, EBSCO, and PsycINFO), was performed. Combinations of search terms were generated by reviewing existing literature and consulting an expert librarian.  Search terms included the names of each tool, adherence, compliance, persistence, and medication adherence. Studies were included if they were conducted after January 2000;  involved the use of an adherence tool recommended by a certified health care professional; and  measured the rate of medication adherence as an outcome. Studies on measuring adherence to vaccines and lifestyle modifications were excluded. RESULTS: Preliminary search yielded 637 articles. Articles were excluded following a title review (552) and an abstract review (43). Forty-two studies met the criteria for full review. Six different adherence tools were used. Of these, 27 studies used telephone and text reminders. Four used educational materials and books while another four used blister packing. Three studies used interactive voice response system, two studies used letters and faxes, and another two studies used pill boxes. Improvement in medication adherence was found in all studies. The largest change in medication adherence was observed through the use of telephone and text reminders. CONCLUSIONS: Medication adherence is a problem that pharmacists are addressing through health care reform legislation. It’s important for pharmacists/researchers to educate about effective adherence tools in order to improve quality of care to patients and society.